The most effective method and apparatus for saturating water with oxygen on an industrial scale is described in international patent application WO 95/29130. (U.S. patent application Ser. No. 08/411,708, now U.S. Pat. No. 5,814,222). According to this known process, water is introduced into a sealed enriching vessel which is under oxygen pressure, the water is subdivided such as by running it over a series of trays and the water is inflowing contact with the oxygen before about up to 55-60 mg/l oxygen is dissolved in the water. Is known method and apparatus works very well, however, it was desired to develop a high capacity, smaller and less costly and more portable apparatus capable of producing on an industrial scale super oxygenized water containing even more oxygen and retaining the dissolved oxygen for longer periods than with the known method.
Effective bioremediation requires a high rate of oxygen use, but replenishment of oxygen occurs very slowly in groundwater. As a result, oxygen levels in the contaminated systems are often quickly depleted, even when water has been thoroughly aerated before the onset of the bioremediation process. Bioremediation processes would be much more effective if oxygen levels could be maintained in the groundwater for a longer period of time after they are aerated. This means both higher concentrations of dissolved oxygen, and a lessened degree of degassing of oxygen from the water.
Groundwater pollution control efforts have generally focused on using various "pump and treat" methods which have met only with very limited success while being extremely costly and time consuming. A later development of bioremediation, also known as in-situ or passive remediation, has recently presented itself as a more cost-effective means of treatment, and is by far the most rapidly expanding sector of groundwater treatment technology. Most bioremediation sites utilize aerobic microorganisms to degrade the contaminants. In some circumstances the contaminants themselves are the primary substrate. However, due to resistance of most synthetic organic chemicals to biodegradation, the microbes often require an additional food source, such a methane or methanol to utilize the contaminants. In any case, the organisms need a surplus of dissolved oxygen to maintain the aerobic conditions necessary for accelerated by biodegradation.
Experience demonstrated to date that the maintenance of adequate dissolved oxygen levels is one of the larger challenges to bioremediation projects. It was determined that the greater the dissolved oxygen content, the greater and more rapid the treatment A study conducted by the U.S. Air Force in 1992 found that with about 35 mg/l dissolved oxygen feed water, an 80% reduction in dichloroethane could be obtained within 150 hours. In a laboratory study in 1993 it was found that vinyl chloride could be reduced by 95% within two weeks by infusing the contaminated groundwater with about 25 mg/l dissolved oxygen. Low dissolved oxygen bioremediation operations have proven to be very slow at best, and completely unsuccessful at worse. For example, in another 1993 experiment it was determined that oxygen levels around 18 mg/l produced little or no reduction in dichloroethane after twelve days.
Four different methods have been employed in the past to introduce oxygen into aquifers: air sparging, electrolysis, hydrogen peroxide, and surface aeration. All of these have limitations. Air sparging in the case of aquifers involved sinking wells into the aquifer to provide contact between the ground-water and the atmosphere. This, however, produces very low oxygen levels, comparable to those that occur naturally, of about 10-14 mg/l in cold water. Electrolysis was not found to offer any practical, real word applications, because concentrations of only up to 16 mg/l could be obtained but at the same time the organisms for the biodegradation became substantially depopulated. Hydrogen peroxide injection seemed promising only at first glance, because oxygen was produced only at ratio of 1:2 and two as high a concentration of hydrogen peroxide was required to arrive at the relatively low obtainable dissolved oxygen level. Furthermore, hydrogen peroxide proved toxic to the biodegradation organisms and the resulting foam and dead organisms clogged the injection wells.
The best remaining known option was above-ground aeration wherein a portion of the groundwater was pumped up, aerated with air or pure oxygen, and injected back in to the aquifer. When using pure oxygen, dissolved oxygen levels of about 35 mg/l have been obtained in 1992, but theme were diluted upon reentering the aquifer.
A direct relationship between the biological activity and the high oxygen levels could be established, and the activity dropped sharply with lower dissolved oxygen levels. The observations have clearly indicated the need for even higher levels of dissolved oxygen for accelerating the bioremediation for more optimum rates.
Oxygenated water, when exposed to ambient atmosphere, will gradually lose the dissolved oxygen content above the amount (about 10-12 mg/l) that can be maintained under atmospheric equilibrium dynamics.